The invention relates to a fuel injection system with an integral controller for changing the fuel-air mixture supplied to the internal combustion engine under the control of an oxygen sensor located in the exhaust gas path of the internal combustion engine (lambda control).
It is known to change the mass ratio of components in the fuel-air mixture supplied to an internal combustion engine in dependence on exhaust gas composition, with the aid of an oxygen sensor located in the exhaust gas stream of the internal combustion engine. The known system usually includes a controller which produces an appropriate increase or decrease of the instanteous fuel quantity added to the combustion air stream and it does so in dependence on the output signal of the oxygen sensor. It is known that this type of adjustment of the mass ratio of the fuel-air mixture may be employed in internal combustion engines using carburetors as well as in those using fuel injection systems. The controllers which change the mass ratio of the fuel-air mixture normally and preferably have integral control behavior so that, when the effective value deviates for an extended period of time, the effort applied to correct the mass ratio increases continually. In a known fuel injection system of this type, the only control effort is that which aims at an air number of .lambda.=1.0. Due to the fact that the characteristic output voltage of the oxygen sensor changes with finite slope, it is possible to obtain a very small change in the air number by varying the triggering level of the subsequent threshold switch, but this permits a change of the air number only in the direction of a richer fuel-air mixture and does not provide the desired range or variation which should be approximately .+-.5% about the value .lambda.=1.0 so that the internal combustion engine might be operated in an arbitrarily selectable region which lies between .lambda.=0.95 up to .lambda.=1.05 while retaining all the advantages of so-called .lambda.-control.